Recently, a Bluetooth or Wireless Personal Area Network (WPAN) technology for establishing a wireless network between a relatively small number of digital devices in a restricted space such as home or small-size office so as to exchange audio or video data has been developed. The WPAN may be used to exchange information between a relatively small number of digital devices within a relatively close distance so as to achieve low power consumption and low-cost communication between the digital devices. The IEEE 802.15.3 approved on Jun. 12, 2003 defines Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for High Rate Wireless Personal Area Networks (WPANs).
FIG. 1 is a view showing the configuration example of a WPAN.
As shown in FIG. 1, the WPAN is a network established between personal devices in a restricted space such as a home, and the devices may directly communicate with each other so as to establish the network and exchange information between applications without interruption. Referring to FIG. 1, the WPAN is composed of two or more user devices 11 to 15 and one of the devices operates as a coordinator 11. The coordinator 11 serves to provide basic timing of the WPAN and to control Quality of Service (QoS) requirements. Examples of the devices include all digital devices such as a computer, a Personal Digital Assistant (PDA), a laptop, a digital television, a camcorder, a digital camera, a printer, a microphone, a speaker, a headset, a barcode reader, a display, and a mobile phone.
The WPAN is an ad hoc network (hereinafter, referred to as “piconet”) which is not designed and established in advance, but is established if necessary without the help of a central infrastructure. A process of establishing one piconet will now be described in detail. The piconet is started when a certain device, which may operate as a coordinator, performs the function of a coordinator. All the devices perform scanning before a new piconet is started or before being associated with the existing piconet. The scanning refers to a process of, at a device, collecting and storing information about channels and determining whether the existing piconet is present. A device which receives an instruction to start a piconet from a higher layer establishes a new piconet without being associated with a piconet which is previously established. The device selects a channel with less interference based on data acquired by the scanning process and broadcasts a beacon via the selected channel, thereby starting the piconet. The beacon is control information which is broadcast by the coordinator in order to control and manage the piconet, such as timing allocation information and information about the other devices within the piconet.
FIG. 2 shows an example of a superframe used in a piconet. The timing control of the piconet is mandatorily performed based on the superframe. Referring to FIG. 2, each superframe is started by a beacon transmitted from a coordinator. A Contention Access Period (CAP) is used for devices to transmit commands or asynchronous data using a contention-based method. A channel time allocation period may include Management Channel Time Blocks (MCTBs) and Channel Time Blocks (CTBs). The MCTB is a period in which control information may be transmitted between a coordinator and a device or between a device and a device, and the CTB is a period in which asynchronous or isochronous data may be transmitted between a device and a coordinator or between different devices. In each superframe, the numbers, the lengths and the locations of CAPs, MCTBs and CTBs are determined by the coordinator and are transmitted to other devices within the piconet via a beacon.
When a certain device within a piconet needs to transmit data to a coordinator or another device, the device requests channel resources used for data transmission from the coordinator, and the coordinator allocates the channel resources to the device within an available channel resource range. If a CAP is present within a superframe and the coordinator permits data transmission in the CAP, the device may transmit a small amount of data via the CAP without the need for the coordinator to allocate a channel time to the device.
If the number of devices within the piconet is small, channel resources used for enabling the devices to transmit data are sufficient and thus no problem occurs in channel resource allocation. However, if the number of devices is large and thus channel resources are insufficient or if a large amount of data such as a moving image is transmitted, the channel resources may not be allocated to the other devices even when the other devices have data to be transmitted.
In a data communication process between two or more devices belonging to the WVAN, communication quality may be deteriorated according to device environment, such as occurrence of an obstacle interrupting communication between devices, change in distance between both devices or locations of both devices or interference between adjacent different devices.
Accordingly, research into a method of smoothly and efficiently perform data communication between devices configuring the WVAN is ongoing.